Human T cells produce soluble, noncytolytic factors (HIV suppressor factors) that suppress the replication of virtually all HIV strains. Numerous clinical studies have shown that an inborn capacity to release high levels of CD8+ T cell-derived factors correlates with better control of HIV infection, In particular, this correlation was observed in a subset of HIV-infected subjects (called long term non progressors or LTNPs) that do not develop AIDS for more than 10 years in the absence of antiretroviral therapy. Since these factors are noncytolytic, broadly active against HIV strains, and associated with non-progression to AIDS, they are potentially valuable resources for the development of new approaches to treat HIV infection. Moreover, the development of new therapeutic agents is now clearly linked to a sustained search for soluble suppressor factors. In 1996, our group identified the chemokines, RANTES, MIP1-alpha, and MIP1-beta as the CD8+ T cell factors responsible for the suppression of "R5" HIV isolates that use the CCR5 coreceptor for entry. This discovery, coupled with seminal studies on CCR5, has led to the development of a new generation of highly promising drugs that interfere with R5 HIV entry. The current goal is to identify the elusive HIV suppressor factors that selectively suppress "X4" HIV strains. This will require novel techniques that avoid the inherent problems of primary cell cultures and optimize the chances for success. Our hypothesis is that we can identify X4 suppressor factors by fractionating conditioned medium from HTLV-immortalized cell lines derived from the T cells of LTNPs. Aim 1 will be to purify and identify soluble X4 HIV suppressor factor(s) secreted by transformed CD4+ and CD8+ T cells from LTNPs. Our newly developed HTLV-1 transformed CD8+ T and CD4+ T cell lines from LTNPs, which consistently release high levels of noncytolytic X4 HIV suppressor activity, will be used to produce serum free conditioned media. This material will be fractionated by affinity chromatography and HPLC and screened for antiviral activity. Amino acid sequence analyses or peptide fragment analyses will used to identify the proteins associated with virus suppression. Aim 2 will be to determine the natural relevance of anti-X4 Factor(s) discovered in Aims 1 to the natural HIV suppressor activity released by primary cells. We will use antibody neutralization and/or depletion experiments to determine whether a candidate factor contributes to the natural suppressor activities of primary cells. Mixtures of cognate antibodies will be used in cases where we have evidence that several antiviral factors mediate redundant antiviral activity.